1. Field of the Invention
The present invention relates to directional drilling and more particularly relates to a system for the drilling of precisely located offset wellbores drilled at a selected radial location with respect to the main wellbore and/or for coring in an oil/gas well, wherein a dual passageway deflection tool allows a packer to be set downstream thereof and a survey tool can be used to select a particular radial position for drilling a selected offset wellbore.
2. General Background
The drilling of offset wellbores is discussed generally in U.S. Pat. No. 4,519,463 entitled "Drainhole Drilling" issued to Frank Schuh and assigned to Atlantic Richfield Company. In the Schuh patent, a method for drilling a well in the earth for producing minerals therefrom is provided wherein a primary wellbore is first drilled into the earth, the primary wellbore being a deviated wellbore having a radius of curvature in the range of from about 2.5 to about 6 degrees per one hundred feet of primary wellbore length, and then drilling from the primary wellbore at least one drain hole wellbore, the drain hole wellbore having a radius of curvature in the range of from about 0.2 to about 3 degrees per one foot of drain hole wellbore length.
Another patent relating to the drilling of offset wellbores is U.S. Pat. No. 4,852,666 issued to Charles Brunet and Alton Watson. The following table lists other patents that relate generally to the drilling of inclined wells, horizontal wells, and offset wells.
______________________________________ U.S. Pat. INVEN- No. TOR TITLE ISSUED ______________________________________ 4,365,676 Boyadjieff Method and Apparatus 12/28/82 For Drilling Laterally From A Well Bore 4,402,551 Wood Method and Apparatus To 09/06/83 Complete Horizontal Drain Holes 4,436,165 Emery Drain Hole Drilling 03/13/84 4,444,265 Schmidt Drain Hole Drilling 04/24/84 4,501,337 Dickinson Apparatus For Forming 02/26/85 And Using A Bore Hole 4,545,435 Bridges Conduction Heating Of 10/08/85 Hydrocarbonaceous Formations 4,573,531 Garkusha Method of Underground 03/04/86 Gasification of Coal Seam 4,598,770 Shu Thermal Recovery Method 07/08/86 For Viscous Oil 4,605,076 Goodhart Method For Forming 08/12/86 Boreholes 4,621,691 Schuh Well Drilling 11/11/86 4,646,836 Goodhart Tertiary Recovery Method 03/03/87 Using Inverted Deviated Holes 4,653,583 Huang Optimum Production Rate 03/31/87 For Horizontal Wells 4,662,441 Huang Horizontal Wells At 05/05/87 Corners of Vertical Well Patterns For Improving Oil Recovery Efficiency 4,682,652 Huang Producing Hydrocarbons 07/28/87 Through Successively Perforated Intervals of A Horizontal Well Between Two Vertical Wells 4,696,345 Hsueh Hasdrive With Multiple 09/29/87 Offset Producers 4,700,779 Huang Parallel Horizontal 10/20/87 Wells 4,705,431 Gadelle Method For Forming A 11/10/87 Fluid Barrier By Means Of Sloping Drains, More Especially In An Oil Field 4,715,452 Sheppard Method of Drilling A 12/29/87 Directional Well Bore 4,714,117 Dech Drainhole Well 12/22/87 Completion ______________________________________
The Boyadjieff '676 patent uses a self-propelled drilling unit.
The wood '551 patent used a cementing step in directional drilling.
The Emery '165 patent relates to the use of a hardening material in directional drilling.
The Schmidt '265 patent relates to a method for drilling into the earth wherein both gas and liquid are produced wherein the earth is treated to render the treated portion essentially impermeable to gas.
The Dickinson '337 patent, assigned to Bechtel National Corp., uses a hollow central pipe disposed in a central passageway in forming bore holes.
The Bridges '435 patent relates to heating of earth formations that involves the application of electrical power.
The Garkusha '531 patent relates to a method of underground gasification of a coal seam and includes steps of igniting the coal and gasifying the same.
The Shu '770 patent relates to a thermal recovery method that uses a plurality of substantially parallel horizontal production wells and a plurality of vertical injection wells.
The Goodhart '076 patent contemplates boring from an essentially vertical hole. The method contemplates drilling upwardly from the vertical hole, a deviated hole into the target zone.
The Schuh '691 patent contemplates the use of separate drilling zones in a grid fashion which do not connect.
The Goodhart '836 patent contemplates us initial vertical shaft as part of its method and also injecting a heating fluid from the surface to the outer loop borehole and directing the heating fluid into a loop comprising the outer loop borehole and the portion of the vertical shaft between the top and bottom of the outer loop borehole with the return of heating fluid to the surface via the vertical shaft.
The Huang '583 patent relates to a method of enhancing recovery of hydrocarbons. The method determines the optimum fluid production rate for a producing horizontal well which will limit the downward movement of the fluid medium towards the horizontal well to a velocity below critical velocity to avoid fingering of the fluid medium through the formation. The critical velocity is defined by a formula.
The Huang '441 patent relates to a modified inverted spot well pattern for recovering hydrocarbons from an underground formation. The method uses a pair or substantially horizontal production wells at each of the four corners of the pattern, the horizontal wells extending from the ground surface and running substantially horizontal distance with the hydrocarbon formation, each pair of horizontal wells forming an x-shaped aerial pattern and a substantially vertical central injection well.
The Huang '652 patent also relates to a method for producing hydrocarbons. Each of those claims includes the use of an injection well.
The Hsueh '345 patent contemplates an injection well as part of a method of recovering petroleum.
The Gadelle '431 patents relates to injecting a fluid into a geological formation or injection wells.
The Sheppard '452 patent uses a multi section borehole which includes a first vertical section. The second section of the borehole has a substantially constant build rate.
The Dech '117 patent uses a casing string composed of alternating casing subs and external casing packer subs.
One of the problems associated with the drilling of offset wellbores is that of accurately positioning the radial location of the wellbore. Another problem is the drilling of offset wellbores not withstanding the orientation of the main wellbore in that the main wellbore may be vertical, inclined, or horizontal.